1. Yes. A computer can absolutely do what Sully did. As long as it's programmed correctly. It's important for the people programming the automation software to do a good job, but an automated pilot is WAY safer than a human. Think about all of the recent plain crashes... one when a depressed human being flew into a mountain. One where a cocky pilot thought he could make a journey without enough fuel.... these were human errors that a computer would NEVER make.
2. Automating the flight of a plane is a lot easier than a car. It's a no brainer. Stuck being Luddites!